There is a continuing need for new antibacterial agents. Although many compounds are known which are useful in the treatment of Gram-positive and Gram-negative bacterial infections as well as other microbial infections, the widespread use of such compounds continues to give rise to resistant strains of microorganisms, i.e., strains of microorganisms against which a particular antibiotic or group of antibiotics, which was previously effective, is no longer useful. Also, known antibiotics may be effective against only certain strains of microorganisms or have limited activity against either Gram-positive or Gram-negative, aerobic or anaerobic organisms.
The therapeutic use of certain quinolizinone derivatives has been described previously. For example, Y. Kitaura et al., in U.S. Pat. No. 4,650,804, issued Mar. 17, 1987, have disclosed quinolizinone compounds having a tetrazolylcarbamoyl substituent which are useful for the treatment of allergic and ulcer diseases. J. V. Heck and E. D. Thorsett, in European Patent Application No. 0308019, published Mar. 22, 1989, have disclosed the use of certain 4-oxo-4H-quinolizine-3-carboxylic acids and derivatives thereof for treating bacterial infections. However, there remains an ongoing need for novel compounds which have improved antimicrobial potency and/or different spectra of activity.